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CrazyisNSFW OP t1_jb4lvdp wrote

Reply to comment by djublonskopf in What's the original function of recurrent laryngeal nerve? by CrazyisNSFW

Thanks for your excellent reply!

Coincidentally, the paper you cited also explained how isolated situs inversus may form; I'm really grateful you posted the link.

Feel free to correct my understanding: As my understanding, lung did not evolve from gill; rather, it's a structure unrelated to gill and innervated differently and recurrent laryngeal nerve then repurposed to innervate various structures on mammalian neck instead.

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djublonskopf t1_jb4tcd3 wrote

Correct. Lungs evolved completely separately from gills. Our ancestors repurposed gills into inner ears, the cartilage of the trachea, and the hyoid bone, all structures still around our jaws/throat.

(Technically, our even earlier ancestors repurposed parts of their gills into the first jaws, too.)

Early in embryonic development, however, our gill arches and their major blood vessels still appear…and the recurrent laryngeal nerve grows out to that embryonic gill tissue. Later in development, the “gills” stay basically in place and become those other structures in the ear and throat. So instead of innervating gills, the nerve is now innervating…all the things we repurposed our gills into.

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atomfullerene t1_jb6jhma wrote

> As my understanding, lung did not evolve from gill

Correct. And as a side note, lots of people will tell you that lungs evolved from swim bladders, but in fact it appears that the reverse is true. Early lungs developed as a pouch off the digestive tract in early fish living in low oxygen waters, and only later did they develop into the specialized swim bladders that many fish have today.

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CrazyisNSFW OP t1_jb7sfrq wrote

That's something new for me. Thanks!

Side question though, can fish absorb oxygen with the swim bladder?

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atomfullerene t1_jb80jaf wrote

Some fish have dual use lung/swimbladders, but a great many common fish have lost the respiration use entirely and the swimbladder often has no open connection at all remaining to the digestive tract. These fish often use other methods if they want to breath air, like the labryinth organ in bettas.

Even fish with totally closed swim bladders can absorb gasses from them into the blood...and push gasses into them from the blood. That's how they inflate and deflate them.

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